Earlier quoted context omitted.
There is a really useful free tier - I think the paid tier mostly includes collaboration features.
I had a recent experience with autodesk that shows that free tiers can disappear or be neutered after you've invested significant time and energy into them. If you just owned that version of the software it would work forever instead you are at the mercy of the platform forever. Caveat emptor
Take a look at Sketch. You can use a file on future versions...but up to a point. If you hit that limit, you will have to buy the upgrade.